1. Field of the Invention
The present invention is directed to a keyless chuck adapted to releasably hold a tool bit such as a drill bit of a power drill or the like rotary power tools, and more particularly to a chuck for rotary power tools capable of reversing the tool bit.
2. Description of the Prior Art
Keyless chucks are known in the art in which a set of gripping jaws are tightened on a tool bit by manipulating a handle ring to rotate independently of a driving connection from a drive source to the tool bit. Such handle ring is generally located around a chuck body which carries the gripping jaws and is adapted to be coupled to a drive spindle of the drive source for establishing the driving connection. The handle ring is rotatable relative to the chuck body and is operatively connected to the gripping jaws in such a way as to tighten and loosen the same on the tool bit upon being selectively rotated in relation to the chuck body. This provision of disposing the handle ring around the chuck body is very likely to be the cause of generating a counter rotating action between the handle ring and the rotating chuck body such that the handle ring is forced to be rotated in the opposite direction to that of the chuck body when the latter is driven to rotate for performing the work with the tool bit. This counter rotation of the handle ring due to the rotation of the chuck body certainly results in the unintended loosening of the gripping jaws, which is accompanied by the rotation of the chuck body in one of the directions of advancing and removing the tool bit into and from a workpiece. In other words, even the handle ring is arranged to counter-rotate in the direction of tightening the tool bit in response to the chuck body being driven to rotate for advancing the tool bit into the workpiece in order to prevent the undesired loosening of the gripping jaws due to such counter rotating action during this tool driving operation, which is usual with the prior keyless chucks, the above undesired loosening is inevitable when the chuck body is rotated in the opposite direction of removing the tool bit from the workpiece. This poses a serious problem particularly when the chuck is utilized in a power tool such as a power drill and a screwdriver capable of reversing the tool bit for removing the tool bit by the use of its power since the resistance or reaction torque applied to the tool bit from the workpiece during this operation is additive to cause the handle ring to counter-rotate in the direction of loosening the gripping jaws, eventually failing to continue the operation of removing the tool bit from the workpiece.